The present invention relates to space and communications satellites, and more particularly, to an optical beam directing apparatus on-board a satellite.
Satellites use radio frequency (RF) communications between the satellite and the Earth. Networks of satellites above the Earth may also communicate with each other via crosslinks. RF communications are possible for intersatellite communications, however, optical communications are preferred.
The advantage of optical intersatellite links over RF links derives from the increased data rates, reduced power consumption, smaller size, and lower weight of an optical telescope versus an RF antenna. As a result, a single satellite can carrymore communication terminals, thereby increasing the overall data-handling capacity.
Optical communications require a means for accurate pointing and tracking for extended periods of time. In known systems, very stable, highly accurate, mechanical gimbaling systems are used to direct the optical beam to its desired location. These mechanical gimbaling systems are mounted on the exterior of the spacecraft. The mechanical gimbal rotates the entire laser terminal to the direction required. Commonly, a painting mirror is used with the mechanical gimbal to acquire and maintain the beam on target. Also, a fast scan mirror is used to compensate for spacecraft motion and vibrations.
There are several drawbacks to a mechanical gimbal system. Commonly, the mechanical gimbal is very complex, very heavy, bulky, and power hungry. Also, an unobstructed volume outside the spacecraft must be provided so that the mechanical gimbal can point the optical telescope in the proper direction.
It is, therefore, one object of the invention to provide an optical communications device that is less resource intensive than those of the prior art. The present invention uses optical methods for beam movement rather than mechanical methods for beam movement as in the prior art.
In one aspect of the invention, a satellite has a satellite body and an optical communications device attached to the satellite body. The optical communications device has a laser light generator, a first optically refracting element optically coupled to the light generator, and a first movement device coupled to the optically refracting device. A second optically refracting element is optically coupled to the first optically refracting element. A second movement device is coupled to the second optically refracting element. A controller is coupled to the first movement device and the second movement device for controlling the relative position of the first optically refracting element and the second optically refracting element.
In a further aspect of the invention, a method for controlling an optical beam from a satellite comprises the steps of generating an optical beam; positioning a first optical device; directing the optical beam through the first optical device; refracting the optical beam; positioning a second optical device; and refracting the optical beam to a predetermined location.
One advantage of the invention is that the optical communication device may be fix mounted to the spacecraft. This eliminates the expensive and bulky rotating devices used in the prior art. This also allows the optical device to be thermally and mechanically isolated from the spacecraft.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.